1. Field of the Invention
In most turbine stages a replaceable radial tip seal is mounted on a stationary shell or diaphragm. The tip seal is positioned to hold a small operating clearance with the rotating blade outer cover or shroud, so as to minimize leakage that would otherwise bypass the rotating blades or buckets. The tip seals usually employ a geometry that includes a thin tooth or teeth that, should a rub occur between the tooth and the shroud of the rotating blade, the tooth could be rubbed away with a minimum of heat and damage to the shroud.
With this arrangement, the leakage steam is forced to pass close to the outer surface of the shroud, usually very close to the tenon that secures the shroud to the rotating blades. In some turbine locations the leakage fluid may also include water droplets or solid particles such as iron oxide or hard particles such as weld beads. These droplets or particles are harmful to the tenons and, if sufficient damage occurs, can allow the shrouds to fly off, causing expensive repairs and lost operating periods.
Where such particles are known to be present, it would sometimes be preferable to position the tip seal on the shroud itself. In this way, leakage steam and any accompanying particles would be predominantly kept in zones where tenon damage would be minimized.
2. Description of the Prior Art
Turbine designers occasionally use such designs as above described. Where used, however, the seal is manufactured as an integral part of the shroud. This means that should a severe rub occur, the tooth damage is very difficult to repair or replace.
Radial seals have been previously mounted on rotating parts; but only in such locations where adequate radial depth is present to permit grooves and locking devices Such radial depth is not present in bucket covers.
On hundreds of exiting turbines, tip seals have been removed to protect the tenon in spite of the serious increase in tip leakage. A simple, low cost, replaceable tip seal that discourages erosion and damage would be beneficial to both old and new turbines.